1. Field of the Invention
This invention relates to a vibration absorbing apparatus which can change vibration absorbing characteristics in accordance with a vibration state of a vibration damping objective to positively absorb the vibration of the objective.
2. Related Art Statement
In engine mounts, power machines and the, like, vibration, and noise are severely restricted because of the demand for high speed and high power, and consequently countermeasure for the reduction of vibrations always are required in connection with the enhancement of performance in the machinery and equipment. A vibration absorbing apparatus (i.e., dynamic damper) has been adopted as a countermeasure for the reduction of vibrations.
In this dynamic damper, additional mass is connected to a vibration damping objective (mass of a main vibration system) through a spring and a frequency of vibration of normal mode in the secondary vibration system consisting of the spring and additional mass is properly selected, whereby the vibration of the objective is mitigated.
In the conventional vibration absorbing apparatus, however, it is necessary to select the additional mass to be at least 10% of the vibration damping objective (main mass), so that there is a problem that the weight of the vibration absorbing apparatus itself becomes heavier.
Furthermore, a large vibration absorbing effect is obtained at a particular frequency range, but this effect rapidly decreases when the frequency is outside the above range and there is rather caused such a phenomenon that the vibration absorption is inversely degraded at both frequency regions outside the aforementioned frequency range.
FIG. 14 shows a side view of the conventional vibration absorbing apparatus, and FIG. 15 is a plan view of FIG. 14.
In FIG. 14, large vibrations are transmitted from a base 1 through a vibration damping member 2 to a vibration damping objective 3, for example, a precision machinery body, a computer or a support therefor.
Although vibration damping is performed at least through the vibration damping member 2, there is a point producing a very large vibration in a certain frequency range, i.e. a resonance point, which can not be removed only by the vibration damping member 2.
As a conventional countermeasure, therefore, a band plate type vibration member 4 or the member 4 having a spring property and provided at each end with an additional mass 5 is attached to the vibration damping objective 3 through a support member 6 to thereby absorb the vibration energy of the vibration damping objective by the vibration system consisting of the spring of the member 4 (bending vibration) and the additional mass 5.
When using such a vibration absorbing apparatus, however, the mass of the secondary vibration system consisting of the spring type vibration member 4 and the additional mass 5 is required to be set to at least 10% of the vibration damping objective 3 (main mass), so that the weight of the vibration absorbing apparatus itself becomes undesirably larger. Also, even if the spring characteristic of the secondary vibration system is properly set, the vibration absorbing effect is merely obtained at the particular frequency range.